title: Interference from Indian diet on the internal standard in a commercial method for the measurement of urinary metanephrines by high-performance liquid chromatography with electrochemical detection.
abstract: BACKGROUND
  Urinary metanephrines are widely used in the diagnosis of catecholamine secreting tumours. Over the past two years we have been using the commercial Recipe(®) ClinRep(®) Complete Kit for Metanephrines in Urine coupled with high-performance liquid chromatography and coulometric detection. It was noticed that the internal standards on the patient chromatograms were sporadically raised due to interference.
  
  
  METHODS
  The interference had identical chromatographic and electrochemical properties to the Recipe(®) internal standard (undisclosed identity). Inspection of the patient names showed it seemingly had a higher frequency and magnitude in patients of Indian origin. The source of the interference was tracked by dietary observation and intervention to curry leaves, a common component of Indian foods.
  
  
  RESULTS
  The interference was chromatographically and electrochemically indistinguishable from the internal standard. The mass spectrum of the pentafluoropropionate derivative of the interference matched the Recipe(®) internal standard and was identified as methoxyhydroxybenzylamine by library match.
  
  
  CONCLUSIONS
  The component co-elutes exactly with internal standard and artifactually decreases the metanephrine and normetanephrine results. It is surprising that it has not been described previously. Patients being assessed for catecholamine secreting tumours should be advised to withdraw from eating Indian foods at least 24 h prior to commencement of urinary collection.
authors.affiliation: Department of Specialist Chemical Pathology, Auckland City Hospital, Auckland, New Zealand.
authors.forename: Hima
authors.initials: H
authors.lastname: Madhavaram
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Woollard
mesh_terms: D016477:Artifacts; D002851:Chromatography, High Pressure Liquid / Q000592:standards*; D004032:Diet; D004563:Electrochemistry / Q000592:standards*; D006801:Humans; D007194:India; D008676:Metanephrine / Q000652:urine*; D012015:Reference Standards; D016482:Urinalysis / Q000592:standards*
chemical_list: D008676:Metanephrine
keywords: Catecholamines; analytes; chromatography; clinical studies; laboratory methods; tumour markers